Why does my system now have shrill top end.

Kosst, my hypothesis is not predicated on the cables having changed in any way whatsoever. If it wasn’t clear, when I referred to the condition being "sufficiently marginal that minor aging effects or perhaps even a change in AC line voltage have put it over the edge," resulting in ringing or oscillation, I was referring to minor aging effects in the amplifier. Which in turn might have made the amplifier more prone to ringing or oscillation as a result of the heavy capacitive load.

Admittedly, though, the fact that both channels are exhibiting the problem does **somewhat** lessen the likelihood of my hypothesis accounting for the problem.

Also, Peter (Pbnaudio), thanks for your comment. As many here are aware, Peter is a highly experienced designer of well regarded audio electronics and speakers.

Regards,
-- Al

Have your listening habits changed? My system sounds much brighter if I listen when I’m fatigued/tired.

Otherwise, it’s most likely that your amp needs service, or you need to listen with a Shakti stone taped to your head.

I have not read every post in this thread, but how old are you, and have you ruled out hearing loss? - Gerry